? about stack size & placement on block/brick arch

[Maplehobbyist]

After having boiled on a turkey fryer in the garage the last two years, I've decided to upgrade a little and make a block and brick arch. The pictures are from the figuring it out process, which I did in the driveway since it was level and near where the tools are. It will be transferred to the sugar shack once I work out the rest of the details, which mainly concern the stack.

1. What size stack?


The combustion area under the front pan is about 15"x13"x10". It seems volume wise, I wouldn't need more than a 4" or 5" pipe, but there may be other reasons for going bigger.

2. Is it better to have the pipe exit from the top or the back?


The metal sheet just behind the back pan is intended for mounting the pipe. This would work well for taking the stack straight through the roof and it also draws the heat along the bottom of the second pan. If I exited from the back, I would just use the metal sheet as a pre-warmer.

3. Should I take the stack straight through the roof or elbow it through the wall, then go up?


Going through the wall will be the easiest for two reasons. It hasn't been built yet so I can basically frame it around the pipe, making sure I've got all the necessary clearances and insulation in place. The other reason is the roofing will be clear plastic corrugated sheets. I'm not sure how easy it will be to make an opening in that kind of material waterproof. Going through the roof would be better for the draw and pretty easy to put the pipe together.

4. Would it be best to fill the hollows in the block with sand/gravel or leave them open?


Filled would be best to keep as much of the heat under the pan but open would be better to make sure the blocks didn't become too hot.

[valleyman]

Hi
Nice looking set up. I made a similar block arch. I'm using 4 rest. pans. I have a 6" dia stack out the back and it gets the pans ripping. It's about 10' tall. If I can be of help let me know.
Greg

[SeanD]

You basically have all the right ideas for a successful set up.

I know your question is about the stack, but you need a taller firebox first. With those pans sitting down into the box and the blocks on the bottom serving as your grate, you only have about the height of that fire brick which I'm guessing is 9". That's not enough room to get wood in there and let that fire breathe. Coals are going to build up quickly and then it will choke itself off. I had the same problem.

The sheet metal door is a great idea, but lift it up so air can get underneath it. Remember, fire lives on air, so give it plenty. It's best if the air comes in under your firebox.

Add one more course of block if it can handle it structurally. You may have to go with full-sized blocks so it's not too wobbly. That will give you 17" of height inside. Also, cut back on the bricks on the bottom and move them to the side. Then run angle iron across the bricks to act as a grate. If enough air is getting in, you won't build up a pile of coals and ash.

I'll look for some pics of some of my trial and error and post them for you.

Sean

[SeanD]

Here are the pictures I mentioned. The first one shows a firebox identical to yours. See how the coals and ash have built up? No air is getting in there and it is a slow burn like a wood stove. The result was a crappy boil.

The second picture shows pieces of metal fence posts cut and laid across the bricks on the sides. Plenty of air can get under all parts of the fire and I had plenty of room for wood.

The third picture shows it in action from underneath. It roared like mad and I was firing every 6 min. I barely had any ash at the end of the boil.

I have a lot more pics of different block arch set ups as I tinkered. Let me know if anything else helps.

Sean

[Maplehobbyist]

Thanks for the replies and the pictures, they help a lot.

With the short width (12") of the first pan, I was worried that the fire would just bypass it on it's way to the stack, if the bottom of the pan was too far away. That's why I only made the whole thing 2 blocks high and arranged the bricks how they are, to basically force the fire up to the bottom to the front pan. I plan to set a mesh grate on top of the bottom course of fire brick and the piece of sheet metal that I'm going to use as a door will have an opening that lines up with the gap in the fire brick at the bottom of the firebox that I will cover/uncover to allow less/more air in depending on how the fire is burning. Would that reduce/eliminate the starved-for-air fire? What if I rearranged to fire brick so the firebox was completely open along the bottom front edge? All of my wood is 12" long and less that 3" in diameter, if that matters.

[Dennis H.]

A 6" stack should be more than enough for your setup.
I would also try to make the opening oval on the plate that you have back there. The more oval/flattened out that you can make the stack the more heat that you will be able to get out to the corners of the back pan.

I would also try and reinforce that plate in the back. The heat will warp and twist that in no time. I would do the same with the door.

Good looking setup, you are on your way to a real nice evap.

[SeanD]

Don't worry about the fire bypassing your front pan. In fact, prepare for the opposite. You are going to have sap flying out of it during your boil. The trick is to get the heat to travel backward to get your back pan boiling. That's where the stack comes in. The draft will pull it back there. With only two pans and dropped in to boot, you are not going to have any problems.

The mesh and door are good ideas. The mesh is going to take an intense amount of heat, so make sure it is thick. The first one I tried was one of those camping grates you can put across a camp fire. It sagged and disappeared by the end of the first boil. Like Dennis mentioned, the door will need to be insulated to withstand the heat. Since it is so small, an easier route might be to just lean a piece of metal against it as a door. I insulated a homemade door from sheet metal and that wasn't too bad (below). It took a beating, but I still have it. You could also install one of those Vogelsang doors, but you'll still need to insulate it.

The opening you have under the brick is too small. It should have a minimum area of whatever your stack is. If you have a 6" stack, that's an area of about 30". So you would need at least a 10" opening 3" high to give it the air it needs. I think those fire bricks are 2" tall? In that case keep the whole 15" width open on the bottom.

It's good you are trying this out now. You have plenty of comfortable time to test boil and maximize your efficiency. I always seemed to be doing it in a foot of snow the day before I tapped. Just dry fit it, like you have and then you can move things around easily for the second test.

Sean

[Maplehobbyist]

It's good to hear you think the heat will stay on the first pan, I was a little apprehensive about putting this thing together and then having it not work.

I've got a feeling the mesh I bought for the grate is not going to do the trick. It's 18 gauge, laid in a pattern that creates diamond shaped openings that are about 1/2" at the widest and 1-1/4" at the longest. Sounds like it may not be long for this world if I use it.

I understand why I would want to insulate the door but I'm at a loss as to how to do it. It seems the insulation should be on the inside, but if I make it too thick it's going to occupy too much of my fire box. Maybe I'll just look for something thicker to lean against the opening. Any ideas where to look for thicker gauge metal? The stuff I'm using came from Lowes but they don't have sheet metal in any thicker gauge than what I got. I could replace the stuff on the top behind the second pan while I'm at it. I'd have to do that before I get the pipe for the stack. So, do they make 8" oval to 6" round adapters?

I'm thankful you gents took the time to reply. It's better to find this stuff out now than in the middle of a boil in the middle of winter in the middle of the night.

[Maplehobbyist]

I'm about to test fire my evaporator and I was just wondering how long of a burn I would need to get an accurate assessment of how many gph's I'm getting? And is plain water good enough or should I dissolve some sugar in it so it's properties more resemble sap?

[Paperman]

Just boil it!! I posted a debate last year if the boil rate slows as sugar content rises. Seems we have good argument both ways so just have at it and enjoy. The longer you can boil the better the average. being the first boil you will try and make it all it can be. Will you do that for the 15 hrs a day you will be boiling in season? My vote is light a fire make it boil, figure where you want to add sap and how you are going to empty the thing. Call it good until spring. You cant tweek and play when you get in the groove of boiling.

[Maplehobbyist]

I'm just trying to figure out how much I can get rid of per hour so I have an idea of how many taps to put in next spring. I was boiling for 15 hours a day on some weekends last year and I don't want to go back there.

I used plain water and boiled for 3 hours. I figure I got right around 4 gph. I think I can get it a bit higher since I didn't get much of a boil in the rear pan and I think I figured out why.

I'm sure glad the maple season doesn't happen in September, it's too d**n hot in the shack.

[Paperman]

"I was boiling for 15 hours a day on some weekends last year and I don't want to go back there."

Dont worry as soon as you figure out how to get the rate up andthe hours down you will start looking for more tree to get the production up and the sleep down.:lol: Just the way it seems to work.:mrgreen:

[Tithis]

I know the feeling. I made a really simple block arch last year and getting a good boil was a pain and it took all day. Near the end of the season I got the hang of it more and was able to build a hotter fire. Huge difference in boiling time.

That's why this coming year I'm putting a big focus on building a good arch. Since I'll be doubling up on the number of taps getting my boiling rate up is essential.

Good luck to you.

[Maplehobbyist]

I noticed that the outside of the blocks under the front pan were cool to the touch for the first couple hours, but warmed up considerably in the third. I assume that happens because the fire brick is absorbing much of the heat, then radiating it out when it can't take any more. Would some kind of insulating material (arch board?) between the fire brick and the cement blocks keep more of the heat under the pan?

As I said before, I didn't get a very good boil on the rear pan (only at the front of it and maybe a third of the way back) and I was wondering if it's because I only have about an inch of space under the entire pan. The flames hit the front side and bottom of that pan when they leave the fire box, which causes it to boil in that area, but there's not enough space under the pan to draw a large enough quantity of exhaust quickly enough to heat the rear of the pan. The flat plate on the rear where the stack is attached never got warm to the touch, which is kind of a bummer since that's where I was hoping to rig up something as a pre-heater.

The rear pan seemed to boil better when I had the water deeper (1.5"+ vs. >1"), which would make sense if most of the heat getting to that pan was hitting the front edge and not traveling along the bottom. The gap between the bottom of the pan and the arch is the same all the way down its length. Would it be better for there to be a bigger gap at the front while keeping it the same at the rear?

[SeanD]

The key piece of info you shared is that back plate. After three hours, it should have been piping hot. Was the stack hot? Something is not right there.

You can definitely ramp or slope the angle leading to the back. That's how most arches are designed. That should give you more flames hitting your back pan. Try that first. It won't cost anything. If that back plate is still cool to the touch, you need a larger or taller stack to draw that heat to the back.

When you opened up your door to fire it, would the flames come toward you or were they curling toward the back? If they came toward the front, your stack is not giving you enough of a draw.

If things are working right, that back plate should be hot in about 30 minutes maybe a little longer - not three hours. If it is still cool after an hour, shut it down and tinker again.

Sean

[Paperman]

Can you peek inside when the fire is ripping and see if there are flames on the pans? With just a flat back pan I dont know how much heat you pulling off just the flat surface. The deeper you run the more wetted surface area you have. Might give you another 30 sq/in of heating area. With only an inch under the bottom you may not have enough room. Do the math and see if that is a choke point. Stack is 28 1/4", and the opening under the pan looks like around 14"? then another 2x1 on the sides. Total of about 18" of area around the pan and 18+ leaving the stack. Choke, Move things around a bit to give it more breathing room.

[Maplehobbyist]

I've attached some pictures that hopefully will help.

I pulled the rear pan off during the boil and there were flames almost to the back end. Not a lot but some. The flames were a V shape with the point centered on the stack. The stack did get warm. Is it possible the exhaust reached the stack in such a narrow stream that it only heated it up and none of it reached that back plate? There's only about 1" of back plate between the rear of the pan and the stack. Where I touched it for sure was on the back left corner. I don't remember if I touched it between the pan and the stack. I do remember smelling smoke after I opened the door to fire it but I attributed that to my poor door design. It's not very airtight, to say the least.

Paperman, not sure what your numbers mean. The opening between the firebox and the rear pan is about 6"h x 14"w, of which the top 2" in blocked by the angle iron that supports the pan. The pan sits 2" below the bottom of that. The fire brick under the rear pan take up a bit over an inch, leaving less than an inch of space between them and the bottom of the pan. The brick in front is centered in the opening, leaving a space about 2" wide on either end. The brick behind that is pushed all the way to one edge, leaving a 4" wide space on the other edge. The brick behind that is pushed to the opposite edge. I'd hoped the alternating pattern would create some turbulence as the exhaust hit the exposed edges of the brick, forcing it to contact the pan. Maybe it just slowed the exhaust so it was too cool by the time it got to the rear of the pan.

My thought is to remove the front brick to create a larger initial opening for the exhaust but leave the others to get it closer to the pan. Actually maybe I should remove all the bricks under the pan. If the boil is better, great. If it's worse I can put some back for the next one. I'm not going to do a another test boil, so I'll just have to wait and experiment during the season.

[Paperman]

"Paperman, not sure what your numbers mean"

My numbers are the area for the openings you have. Stack has an open area of (6" stack /2=3R 3rx3r=9 9x3.14=28.26") 28.26" of open area. Your open area around the pan seems to be less than that by a good margin. Place your pan in the arch and measure your area of the flue gas path. Its hard to get the stack to pull (draft) the fire to the rear if your choking the air flow in the middle of the arch. 10# of sheet dont fit throgh a 5# hole. From the pics you are carrying alot of soot/unburned carbon to the back. thats fuel not burned. More air more heat from the same fuel. I would pull alll the botom blocks and try it.

[Maplehobbyist]

Thanks for the explanation, that really makes sense. If I pull the blocks under the pan I should have about 28sqin in both areas.

Dang, now I'm fired up! Wish I could go test boil it now. Wonder what the boss would think if I came in all sleepy-eyed and smelling like wood smoke--oh, she'd think it was sugaring season.

[Paperman]

Come on man almost a week and nothing:cry: Were doing so good. Maybe he got it rolling so good he doesnt want anybody else to know how its done.:lol:

[Maplehobbyist]

...Maybe he got if rolling so good he doesn't want anybody else to know how its done.:lol:

I wish.

I've just been busy doing all those other necessary things-cutting, splitting, stacking. Haven't used wood to boil with in a few years, not sure how much I will need. Punch-list for the shack. Still need a door, some shelving, not sure what I'm putting up as siding so that will probably wait til next year. I'd post some pictures of it but after looking at some of the sugar palaces that others have built, I'm kind of embarrassed for it.

Not going to do any more test boils, we've got real hard water around here, so cleaning the mineral deposits out of the pans from the last test boil was a bit of a pain. A bit of vinegar, a scotchbrite pad and a lot of effort took care of it, though.

I do want to say thanks to all who gave advice, though. It's great to have a place like this, where people are willing to share their knowledge, so everything doesn't have to be learned through trial and error and error and error.

[SeanD]

Paperman has it right. Your pictures tell the whole story. I have a bunch just like them myself - soot all over the bricks. You definitely have enough air getting into the firebox because the bricks in the firebox are clean. Then it is getting choked off in the back section and that soot is building up. Open that area up a little more and you should be good. How tall is your stack?

You can also flip the bricks over to get a fresh start. Once I built that soot up, it was hard to get rid of the smoke smell during the boil.

Let us know how it goes. We're living vicariously through you as we wait for the next season.

Sean

[Maplehobbyist]

Well, in spite of what I said in my last post, I did do another test boil. I'm pretty confident in my numbers, so I was wrong when I previously thought I was getting 4gph. Here are my notes:


10:50 - fire started, 1 gallon in each pan (2gal), about 1" depth
11:00 - front pan boiling, rear pan small bubbles
11:05 - front pan boiling (Pic #1), rear pan boiling
11:06 - sprint to house for new batteries for camera
11:09 - stack warm, back plate slightly warm, add 1/2 gal (2.5gal)
11:10 - both pans boiling (Pic #2)
11:13 - add 1/2 gal (3gal)
11:17 - shack full of steam, opened all windows open
11:18 - rear pan
11:21 - add 1/2 gal (3.5gal)
11:25 - outside of blocks still cool, stack too hot to touch, back plate warm to touch
11:28 - add 1/2 gal (4gal)
11:32 - removed rear pan (picture didn't turn out), need handles on pans
11:34 - loaded wood
11:38 - removed rear pan again (Pic #3), really need handles on pans
11:40 - rear pan boiling (Pic #4)
11:41 - add 1/2 gal (4.5gal)
11:43 - back plate too hot to touch, outside of blocks still cool but warmer
11:47 - add 1/2 gal (5gal)
11:50 - 1 hour in
11:52 - loaded wood
11:54 - outside of blocks on front pan warm to touch, blocks on rear pan still cool
11:55 - add 1/2 gal (5.5gal)
11:59 - loaded wood
12:03 - add 1/2 gal (6gal)
12:05 - blocks on rear pans warming slightly, still cool to touch
12:08 - both pans boiling nicely
12:11 - add 1/2 gal (6.5gal)
12:13 - loaded wood
12:15 - front block on rear pan slightly warm to touch, rear block on rear pan still cool
12:18 - add 1/2 gal (7gal)
12:19 - loaded wood
12:25 - add 1/2 gal (7.5gal)
12:26 - loaded wood
12:28 - switch pre-heater can to front pan in attempt to increase boil rate in rear pan, both pans depth 1.5"
12:29 - blocks on front pan too hot to touch, rear blocks same as 12:15
12:32 - rear pan, slow boil all the way to back
12:33 - add 1/2 gal (8gal)
12:35 - loaded wood
12:41 - loaded wood
12:42 - add 1/2 gal (8.5gal)
12:44 - rear blocks same as 12:15
12:48 - add 1/2 gal (9gal)
12:50 - 2 hours in, front & rear pans boiling (Pic #5)
12:52 - add 1/2 gal (9.5gal)
12:53 - loaded wood
12:56 - front blocks on rear warmer, rear blocks on rear still cool
13:00 - loaded wood
13:01 - add 1/2 gal (10gal)
13:03 - moved pre-heater so it's balancing on both pans, both pans depth 1.5"
13:04 - loaded wood
13:10 - loaded wood
13:11 - add 1/2 gal (10.5gal)
13:13 - loaded wood
13:17 - loaded wood
13:21 - add 1/2 gal (11gal), loaded wood
13:27 - loaded wood
13:29 - add 1/2 gal (11.5gal)
13:30 - no change in blocks temps
13:35 - add 1/2 gal (12gal)
13:38 - loaded wood
13:45 - pre-heater out, both pans boiling (Pic#6)
13:50 - test boil over (2 gal liquid still in pans)
13:52 - area under rear pan (Pic #7)
13:54 - firebox (Pic #8, 9)
13:56 - end result of test boil (Pic #10)

Pictures 6-10 in subsequent post.

[Maplehobbyist]

Pictures 6-10.

[Paperman]

When you siad hard water I thought how hard can it be. Now I see a jar full of tan stuff:mrgreen:. Good work. I see the brick in teh center is gone and the flame seems to be liking the extra air flow. You can see where it goes dirty pretty nicely. Makes a good argument on why people say you need a full width rear stack. pretty clear the flame is looking for the outlet in the center.

[Maplehobbyist]

Yeah, I was pretty surprised that the bricks under the rear pan wear as clean as they were in that picture. I took a picture showing the same spot about 6 minutes earlier that had much more soot and not nearly as much flame, but it didn't turn out. Maybe I need something in the center towards the back of that area under the rear pan to force the exhaust to the outside.

I was also surprised that I didn't get a higher boil rate. The rear pan boiled quite well except where I had the coffee can pre-heater sitting in it. I think I really need to come up with a different arrangement for preheating the sap. The water I was adding out of the can was never very warm. The problem is there really is no good flat spot on which to set a container that will get very warm. The stack is the only thing close to the evaporator that is hot, so maybe it has to be some tubing twisted around that. Is copper the best thing to use for that?

[SeanD]

Very nice! You've worked out the major kinks. Four to five gallons per hour for those two pans is about right. If you are looking for more, just extend the length of the arch and add another pan. You'll get another 2 gph from the same amount of wood and time. That hot stack tells me there is more heat to take advantage of before it leaves.

Once you have sap going in, you may want to run it a little deeper. The sides of your pans are right in the firebox and will scorch the sap that splashes up on them. When people say they run their pans about an inch deep, that's a different set up entirely. You can go 4-5 inches and not lose any gph. You might actually gain some. When you sink the pan into the firebox, it's like having a single-flue flue pan. Deeper pans will also make it easier to ladle your sweet forward.

There are a bunch of threads on preheating by wrapping the pipe with copper coil. They say a preheater only increases gph by 10%. A third pan will give you a 50% increase, a fourth pan a 100% increase, a fifth pan...

Sean